TIL: Steam is responsible for roughly 0.5% of global internet traffic

 This website lists the global Steam download bandwidth as something in the order of 1.5 Tbps

http://store.steampowered.com/stats/content/

As you can see from this source, the global internet traffic per month in 2015 is roughly 94 Exabytes (couldn't find more up-to-date global estimates)

 http://www.statista.com/chart/624/global-ip-traffic-per-month-from-2011-to-2016/

So the monthly download size from Steam alone is: 1.5 / 8 (bit to Byte) * 60 (minute) * 60 (hour) * 24 (day) * 30 (month) / 1000 000 (TB to EB)or 0.486 ExabyteWhich gives us a ratio of 0.486 / 93.8 = 0.518 %Fairly certain it went down from when I did my estimates a few years ago and got something like 2% (damn HD video streaming). 

Pretty impressive still, and probably the motivation behind staggering releases like Fallout 4 and XCOM 2.